Classical alkylating agents evidently produced their therapeutic as well as their mutagenic and carcinogenic effects by attacking the DNA of target cells. Their therapeutic properties are probably closely related to their ability to produce crosslinks and resistance may develop in cells that can repair this damage. Nitrosoureas, such as bis-chloroethyl-nitrosourea (BCNU) and chloroethyl-cyclohexyl-nitrosourea (CCNU), also react with nucleic acids and produce crosslinks. Previous studies from this laboratory have identified some of the nucleoside derivatives which are produced; the structure of other nucleoside derivatives and, particularly, the nature of crosslinks produced by the nitrosoureas will be investigated in this research project. Synthetic polynucleotides will be used as models for nucleic acids in these studies so that effects on particular nucleosides can be studied separately. Since these polymers are effectively replicated by RNA polymerase, modified and unmodified polymers can be compared to determine which reactions are biologically significant. By obtaining data on different classes of agents - for example classical alkylating agents in comparison with nitrosoureas - 3e will look for explanations of the clinically observed differences among the agents. Some of the modified nucleosides which we have identified in the initial period of this grant are now ready for animal testing as antitumor agents in their own right. Thus, fluoroethyl-guanosine, which has been identified as a product of the reaction between BFNU and guanosine, has shown activity against P-388 cells. Other derivatives will also be tested as they are identified and synthesized. These studies will serve the dual purpose of elucidating the mechanism of action of the parent compound and possibly uncovering new antitumor agents. Although major emphasis will be placed on the therapeutic value of these agents, attention will also be paid to possible mutagenic and carcinogenic side reactions.